1. Field of the Invention
The present invention is related to antennas, and more particularly, to broadband dual polarized antennas composed of oppositely sensed spiral metallizations.
2. Description Of The Related Art
Due to the unprecedented variety of electromagnetic signals in use today, a need has arisen for a single, broadband antenna that will transmit and receive many signals, including not only vertically and horizontally polarized signals, but right-hand and left-hand circularly polarized signals. The need for such antennas is especially strong in applications where size is also an important consideration. Size is an important factor for antennas mounted on mobile platforms, such as aircraft and the like. At the same time, such antennas must not interfere with the aerodynamics of the mobile airborne platform and, for airborne platforms associated with military or security objectives, such antennas must have low observability characteristics.
The sinuous antenna has been proposed as a solution to these requirements. The sinuous antenna is planar, broadband and dual polarized from a single aperture. However, the sinuous antenna has several drawbacks, not the least of which is that it is difficult to construct. The sinuous antenna includes at least four separate antenna arms on its planar surface. The antenna arms radiate out in identical sinuous patterns symmetrically about a center point. The antenna arms cannot contact each other, and each antenna arm must be center fed independently of the others. Given the close proximity of the centers of the arms, the design does not lend itself to low cost manufacturing schemes. This is further complicated by the fact that the ability of such antennas to receive or transmit high frequency signals is determined by the accuracy of the antenna arms near the center of the antenna. Accordingly, as high accuracy is required of the centers of the separate antenna arms, and each antenna arm must be center fed, construction constraints necessarily either diminish the high end abilities of sinuous antennas and/or make construction of sinuous antennas more difficult and costly.
Further, sinuous antennas need additional circuitry, in the form of a hybrid circuit connected to the center feeds, to receive right-hand and left-hand circularly polarized signals. This additional hardware adds to the cost of the antenna, and requires additional manufacturing steps. Therefore, while theoretically effective, the sinuous antenna is complex and difficult to construct.